Shaykh Al-Islām Ibn Taymiyyah said:
The one who refutes the people of innovation is a mujāhid, to the extent that Yahyā ibn Yahyā used to say: “Defending the Sunnah is better than jihād.”
Majmūʿ Al-Fatāwā (4/13)
Sunnah Jihad
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ʿAlī ibn Abī Tālib said:
You will first be defeated at jihad with your hands, then jihad with your tongues, then jihad with your hearts. Any heart that does not recognize good nor denounce evil will be turned upside down.
Al-Muṣannaf by Ibn Abī Shaybah (38733)
Jihad
Al-Imām Al-Awzāʿī said:
Stick firmly to the narrations of the Salaf even if people reject you. And beware of the opinions of men even if they adorn it for you with beautiful speech.
Ash-Sharīʿahʾ by Al-Ājurrī (127)
Sunnah
Abū Al-Wafāʾ Ibn ʿAqīl Al-Ḥanbalī said:
We seek refuge with Allāh from adopting a Maḏhab (position or doctrine), then seeking to validate its basis or search for its evidence.
Al-Wāḍiḥ fī Uṣūl Al-Fiqh (1/259)
Sunnah